In a mobile communications system, a carrier spectrum for data transmission is divided into three parts: a frequency division duplexing (FDD) uplink frequency band, a time division duplexing (TDD) frequency band, and an FDD downlink frequency band. In FDD, uplink data is permanently transmitted in an FDD uplink frequency band, and downlink data is permanently transmitted in an FDD downlink frequency band. In FDD, data uplink transmission and data downlink transmission are separately performed by using two frequency bands of different frequencies. In TDD, uplink data and downlink data are both transmitted in a TDD frequency band, and uplink data and downlink data are separately transmitted in different timeslots by using a TDD frequency band.
As shown in FIG. 1, to avoid interference between FDD uplink data transmission and TDD downlink data transmission, there is a guard band of a particular width between an FDD uplink frequency band and a TDD frequency band. Similarly, to avoid interference between TDD uplink data transmission and FDD downlink data transmission, there is also a guard band of a particular width between a TDD frequency band and an FDD downlink frequency band.
One TDD frame consists of 10 subframes, where some subframes are uplink data, and some subframes are downlink data. As shown in FIG. 2, there are seven subframe uplink-downlink configuration relationships in total, where the black represents a downlink data frame, the grey represents an uplink data frame, the white represents a gap, and the stripe represents a special subframe. If TDD frames transmitted by two adjacent frequency bands within a TDD frequency band use different subframe uplink-downlink configuration relationships, there is interference into each other when subframes transmitted by two adjacent data transmission frequency bands are in different directions. Therefore, a guard band of a particular width also needs to be added between two adjacent data transmission frequency bands within the TDD frequency band.
Although interference occurring when data in different directions are transmitted in adjacent frequency bands can be avoided by using a guard band, the guard band causes waste of frequency resources.